The present invention relates to a method for feeding signatures on to a sewing machine.
Book sewing machines generally present an input conveyor defined by a fixed, usually triangular-section saddle, the top edge of which presents a groove housing the top portion of a loop conveyor. This presents a number of equally-spaced pushers separated by a distance greater than the maximum signature length feedable on to the sewing machine. Each pusher moves upwards out of said groove, and acts as a push member for a respective signature lying astride the fixed saddle, with its back lying along the top edge of the same.
The signatures are fed successively on to the aforementioned input conveyor by means of a feeder usually comprising an input feedbox designed to accommodate a signature lot; a withdrawal assembly for withdrawing the signatures one by one from the feedbox; a "parting" conveyor system designed to successively receive and feed the signatures on to the sewing machine conveyor, prior to which, the signatures are successively engaged by a number of suction heads with suckers, for opening (to the center) the two halves of the signature; and an output feed assembly for receiving the signatures opened on the pusher conveyor, and successively feeding the same on to the fixed saddle of the sewing machine input conveyor.
As regards location of the pusher conveyor in relation to the fixed saddle on the sewing machine input conveyor, two feed device configurations are generally employed: one wherein the transport conveyor is located in line with the input saddle, and the other having a transport conveyor extending substantially crosswise in relation to the saddle.
With an in-line feed device configuration, the assembly consisting of the feeder and sewing machine presents a straight, relatively long structure, which poses numerous problems in terms of operation and floor space. Such a machine, in fact, not only demands extensive floor space, but, being usually run by one operator, involves a good deal of legwork, which often precludes immediate action in the event of malfunctioning.
With a transverse feeder configuration, on the other hand, the feeder-sewing machine assembly presents a substantially L-shaped, far more compact structure, better suited to single-operator control, by reducing the walking distance between the feeder and sewing machine, and so simplifying operation and enabling immediate action in the event of malfunctioning.
The technical scope of the present invention relates to feeders of the second, i.e. transverse configuration, type.
Known transverse feeders generally operate according to the Dolfini method described in U.S. Pat. No. 3,661,379. According to this method, the signatures, initially packed inside a feedbox, are successively withdrawn from the same and fed, equally spaced with their backs facing rearwards, on to a grip type conveyor on which they are fed in a direction perpendicular to the backs, and successively engaged by a number of suction heads mounted for rotation about fixed shafts extending transversely in relation to the travelling direction of the conveyor. A first suction head engages the outer surface of the top sheet of the signature, which, by virtue of combined upward rotation of the suction head and forward travel of the signature, is raised so as to at least partially uncover the bottom sheet (if any) of the top half of the signature, which bottom sheet is then engaged by the next rotary suction head. In actual practice, pending engagement of the next sheet by a respective rotary suction head, each sheet may be maintained in the raised position by a retractable supporting plate. The combined action of the suction heads and respective retractable supporting plates provides for parting the two halves of the signature, which, at a curved end portion of the grip conveyor, is gripped along the front edge of the bottom half, and transferred, so parted, on to the fixed saddle of the sewing machine input conveyor.
Signature feeders operating according to the Dolfini method present a number of drawbacks, which are manifested in direct proportion to the operating speed of the sewing machine. On such feeders, in fact, the signatures on the grip conveyor are aligned perpendicular to the backs and relatively far apart, due to the grip spacing on the conveyor being greater than the maximum signature width feedable on to the sewing machine. Said grip spacing, which is unavoidable for preventing even partial overlapping of the signatures, and so ensuring efficient operation of the rotary suction heads, results in relatively high operating speed of the grip conveyor, and in suction head-signature sheet engagement times inversely proportional to the operating speed of the sewing machine. Moreover, high-speed signature feed involves serious difficulties as regards operation of the retractable supporting plates, each of which has to engage the signatures as soon as a respective sheet is raised by a respective suction head, and then withdraw fast enough to prevent tearing the back of the signature.
For sewing machines operating over a given speed, therefore, the reliability of known transverse feeders of the aforementioned type becomes unacceptable, in addition to the possibility of the signatures being damaged during the parting operation.